This invention relates to swash-plate type compressors for use in air conditioning systems for automotive vehicles, and particularly to double-acting pistons which are placed within cylinder bores formed within the compressors for sliding in the cylinder bores in unison with the rotation of the swash plate.
A conventional swash-plate type compressor used in an air conditioning system for automotive vehicles generally includes double-acting pistons slidably received within cylinder bores formed within the cylinder blocks forming the framework of the compressor, and a swash plate secured on the drive shaft extending through the cylinder blocks and engaging the pistons. The pistons each comprises a casting formed integrally with two piston heads at its opposite ends and an intermediate coupling part coupling the piston heads to each other. The intermediate coupling part has an axially central portion formed with a recess in which the swash plate is engaged. This recess traverses the axially central portion of the intermediate coupling part and has opposite end walls formed with ball pockets. The swash plate has a peripheral fringe engaged within the recess via balls received in the ball pockets and shoes held between the balls and the opposite side surfaces of the swash plate. With this arrangement, when the drive shaft rotates, the swash plate is correspondingly rotated while sliding relative to the shoes to cause reciprocal motions of the pistons for compressing fluid such as refrigerant.
Since the cylinder blocks and the pistons are each formed of a one-piece casting, they should not be made of a metal having a large specific gravity such as steel, in view of the castability of steel and the necessity of obtaining a lightweight compressor. Therefore, the cylinder blocks and the pistons are both formed of aluminum alloy castings.
The conventional swash-plate type compressor having the above construction has the following drawbacks:
1. The cylinder blocks and the pistons which are both made of an aluminum alloy are apt to adhere to each other when heated, often causing seizure between the piston heads of the pistons and the cylinder bores. PA1 2. At the portion where each piston engages the swash plate many parts are used which include balls and shoes. The balls and the shoes may easily slip off the swash plate and the piston in mounting them, thus making the assembly operation troublesome and time-consuming.